Aerostatic lighter-than-air airships have seen substantial use since 1783 following the first successful manned flight of the Montgolfier brothers' hot air balloon. Numerous improvements have been made since that time, but the design and concept of manned hot air balloons remains substantially similar. Such designs may include a gondola for carrying an operator and passengers, a heating device (e.g., a propane torch), and a large envelope or bag affixed to the gondola and configured to be filled with air. The operator may then utilize the heating device to heat the air until the buoyant forces of the heated air exert sufficient force on the envelope to lift the balloon and an attached gondola. Navigation of such an airship has proven to be difficult, mainly due to wind currents and lack of propulsion units for directing the balloon.
To improve on the concept of lighter-than-air flight, some lighter-than-air airships have evolved to include propulsion units, navigational instruments, and flight controls. Such additions may enable an operator of such an airship to direct the thrust of the propulsion units in such a direction as to cause the airship to proceed as desired. Airships utilizing propulsion units and navigational instruments typically do not use hot air as a lifting gas (although hot air may be used), with many operators instead preferring lighter-than-air lifting gases such as hydrogen and helium. These airships may also include an envelope for retaining the lighter-than-air gas, a crew area, and a cargo area, among other things. The airships are typically streamlined in a blimp- or zeppelin-like shape (also known as “cigar” shaped), which, while providing reduced drag, may subject the airship to adverse aeronautic effects (e.g., weather cocking and reduced maneuverability).
Airships other than traditional hot air balloons may be divided into several classes of construction: rigid, semi-rigid, non-rigid, and hybrid type. Rigid airships typically possess rigid frames containing multiple, non-pressurized gas cells or balloons to provide lift. Such airships generally do not depend on internal pressure of the gas cells to maintain their shape. Semi-rigid airships generally utilize some pressure within a gas envelope to maintain their shape, but may also have frames along a lower portion of the envelope for purposes of distributing suspension loads into the envelope and for allowing lower envelope pressures, among other things. Non-rigid airships typically utilize a pressure level in excess of the surrounding air pressure in order to retain their shape, and any load associated with cargo carrying devices is supported by the gas envelope and associated fabric. The commonly used blimp is an example of a non-rigid airship.
Hybrid airships may incorporate elements from other airship types, such as a frame for supporting loads and an envelope utilizing pressure associated with a lifting gas to maintain its shape. Hybrid airships also may combine characteristics of heavier-than-air airship (e.g., airplanes and helicopters) and lighter-than-air technology to generate additional lift and stability. It should be noted that many airships, when fully loaded with cargo and fuel, may be heavier than air and thus may use their propulsion system and shape to generate aerodynamic lift necessary to stay aloft. However, in the case of a hybrid airship, the weight of the airship and cargo may be substantially compensated for by lift generated by forces associated with a lifting gas such as, for example, helium. These forces may be exerted on the envelope, while supplementary lift may result from aerodynamic lift forces associated with the hull.
A lift force (i.e., buoyancy) associated with a lighter-than-air gas may depend on numerous factors, including ambient pressure and temperature, among other things. For example, at sea level, approximately one cubic meter of helium may balance approximately a mass of one kilogram. Therefore, an airship may include a correspondingly large envelope with which to maintain sufficient lifting gas to lift the mass of the airship. Airships configured for lifting heavy cargo may utilize an envelope sized as desired for the load to be lifted.
Hull design and streamlining of airships may provide additional lift once the airship is underway. For example, a lenticular airship may have a discus-like shape in circular planform where the diameter may be greater than an associated height. Therefore, the weight of an airship may be compensated by the aerodynamic lift of the hull and the forces associated with the lifting gas including, for example, helium.
However, a lighter-than-air airship may present unique problems associated with aerodynamic stability, based on susceptibility to adverse aerodynamic forces. For example, traditional airships may typically exhibit low aerodynamic stability in the pitch axis. Lenticular shaped bodies may be aerodynamically less stable than either spherical or ellipsoidal shaped bodies. For example, the boundary layer airflow around the body may separate and create significant turbulence at locations well forward of the trailing edge. Therefore, systems and methods enhancing aerodynamic stability may be desirable.
Further, increasing flight controllability may be another challenging but important aspect for lighter-than-air airship design. For example, the airship may be lifted by thrust forces generated by vertically-directed propulsion engines, and may move forward or backwards powered by thrust forces generated by horizontally-directed propulsion engines. In traditional airship flight control systems, however, propeller pitch has not been variably adjustable. Therefore, the operator of such airships could not control a pitch angle and/or a lift force, among other things, associated with the airship through adjustment of propeller pitch. Further, vertically- and horizontally-directed propulsion engines have been separately controlled, without provision for coordination of these engines with horizontal and vertical stabilizer systems. Therefore, traditional airship controls have not provided maneuverability and response desired by operators. In addition, the operator may wish to know certain flight-related parameters during the flight without having to look away from the view ahead of the airship, to provide more effective control input. For example, the operator may desire an indication of the attitude of the airship to be viewable directly in line of sight (LoS) through a gondola canopy before providing pitch/roll control inputs to the airship. Accordingly, systems and methods for enhancing flight controllability including but not limited to, airship pitch and yaw control, coordination of one or more control systems, and/or indication of certain airship status parameters, may be desirable.
The present disclosure may be directed to addressing one or more of the desires discussed above utilizing various exemplary embodiments of an airship.